A common cooling system for a liquid-cooled internal combustion engine that powers a motor vehicle comprises a radiator behind which is a fan that may be engine-driven. A pump that may also be engine-driven circulates engine coolant from the engine to the radiator and back to the engine. Coolant that has been heated by the running engine gives up heat to the radiator core through which the fan draws air to aid heat transfer from the core to the air.
Certain motor vehicles, like some large trucks for example, have occupant compartments (cabs) that include at least a driver's compartment and sometimes a sleeper compartment behind the driver's compartment. One way to provide cold weather heating for an occupant compartment is by allowing the engine to idle while the vehicle is parked so as to keep the engine coolant sufficiently hot for adequate heating by an occupant compartment heater through which the coolant is circulated. That however is wasteful of fuel because it necessitates running the engine.
An on-board auxiliary coolant heater can instead provide ample heating without running the engine. This is sometimes referred to as “no-idle” heating. One brand of commercially available heaters offers sizes whose heat output ranges from 5,500 BTU to 120,000 BTU, operate on either 12 volts or 24 volts, and can run on gasoline or diesel fuel that is carried by the vehicle. An auxiliary coolant heater may alternatively or additionally be used for engine pre-heating.
A typical auxiliary coolant heater is reasonably compact and contains components necessary to heat and circulate engine coolant while the engine is off. The heater may provide heat at different selectable levels, and may be under the control of an associated control unit to maintain a set temperature.
When occupant compartment heating is called for, a coolant pump starts circulating coolant. A heating device heats the coolant as it circulates so that heated coolant flows out of the heater.
There are various types of auxiliary coolant heaters including those that use fuel carried by the vehicle, those that have electric heater elements, and generators.